This invention relates to a process for making an elastically stretchable composite sheet which is suitable, for example, for a topsheet of a sanitary article such as a disposable diaper, a menstruation pad or the like.
An elastically stretchable composite sheet for a topsheet of a sanitary article is well known which comprises an elastically stretchable sheet and an inelastically stretchable sheet-like fibrous assembly bonded to each other. An example of the process for making such a composite sheet of prior art comprises steps of bonding the elastically stretchable web and the inelastically stretchable web made of fibrous assembly to each other intermittently in one direction, stretching the elastically stretchable web in the one direction together with the inelastically stretchable web and relieving this composite web of tension so that the composite web may contract substantially to its initial length under a contractile force of the elastically stretchable web.
The composite sheet obtained in this manner can eliminate a rubber-like touch by covering the elastically stretchable sheet having such uncomfortable touch with the inelastically stretchable fibrous assembly free from such touch. Furthermore, such composite sheet contracts with component fibers of the fibrous assembly remaining stretched and therefore a bulkiness increases as it contracts. This means that the composite sheet covered with the fibrous assembly can offer a comfortably soft touch.
However, the process for making the composite sheet is accompanied with a problem that both the elastic web and the inelastic web are deformed as these webs are stretched in the one direction. Such deformation reduces dimensions of these webs as measured orthogonally to the direction of stretching. During this deformation, a stretching ratio of the component fibers in the fibrous web remarkably increases along side edges of this web extending in the direction of stretching but not in its intermediate zone. Consequently, in the composite sheet obtained by this process, a bulkiness of the inelastic web comprising the fibrous assembly can not be uniform transversely thereof.
It is an object of this invention to provide a process for making the composite sheet enabling the inelastic web in the form of fibrous assembly to have a uniform bulkiness in the composite sheet including such inelastic web.
According to this invention, there is provided a process for making an elastically stretchable composite sheet comprising an elastically stretchable web having upper and lower surfaces and being continuous in one direction and an inelastically stretchable web made of stretchable continuous fibers and being continuous in the one direction, the inelastically stretchable web being bonded to at least one of the upper and lower surfaces of the elastically stretchable web, the process comprising the steps of stretching this composite web in the one direction and leaving the composite web contract under contractile force of the elastically stretchable web to obtain the composite sheet adapted to be more than the composite web.
The process for making an elastically stretchable composite sheet further comprises the composite web being continuously fed in the one direction to at least two nip roll pairs adapted to rotate at a peripheral speed increasing ahead with respect to a machine direction, the stock web being brought into contact with peripheral surfaces of each nip roll pair so that, in at least one roll of each roll pair, the composite web is brought into contact with this roll over an area of its peripheral surface defined by a quadrant of its circular cross section or larger area until the composite web is stretched to a desired ratio.